Handle for straddled vehicle, straddled vehicle and method for producing handle pipe for straddled vehicle

ABSTRACT

A handle includes handle grips and a handle pipe including an attachment portion, a first grip portion, a second grip portion, a first bent portion between the attachment portion and the first grip portion, and a second bent portion between the attachment portion and the second grip portion. The first grip portion includes a first overlapping region overlapping a first handle grip and a first non-overlapping region not overlapping the first handle grip. The second grip portion includes a second overlapping region overlapping a second handle grip and a second non-overlapping region not overlapping the second handle grip. The first and second non-overlapping regions each include a thick portion having a thickness larger than, or equal to, a thickness of the attachment portion. The first and second overlapping regions each include a thin portion having a thickness smaller than the thickness of the thick portion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of the earlier filing date ofJapanese Application No. 2017-114742, filed Jun. 9, 2017, the content ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a handle for a straddled vehicle, andalso to a straddled vehicle, and a method for producing a handle pipefor a straddled vehicle.

2. Description of the Related Art

A handle for a straddled vehicle includes a handle pipe and a handlegrip. The handle pipe (also referred to as a “handle bar”) is atube-type member mainly formed of a metal material. The handle grip isto be gripped by a rider, and is attached to each of two ends of thehandle pipe.

The handle for a straddled vehicle is available in a type in which thehandle pipe has the same outer diameter entirely and a type in which acentral portion of the handle pipe has an outer diameter larger thanthat of each of the two ends thereof. The latter type is referred to asa “tapered handle”, and is used for, for example, an off-roadmotorcycle. U.S. Pat. No. 5,117,708 discloses a handle pipe for atapered handle.

In the handle pipe disclosed in U.S. Pat. No. 5,117,708, both of twoends thereof are each thicker than a central portion thereof. A handlepipe having such a thickness distribution is produced by, for example,swaging (diameter contraction of the two ends thereof).

Recently, a straddled vehicle such as a motorcycle or the like isdesired to be further reduced in weight. The present inventors madestudies from various points of view for reducing the weight of thehandle. Since there are restrictions imposed by standards or the like onthe outer diameter of the handle pipe, the present inventors attemptedto reduce the weight of the handle by thinning the handle pipe.

However, it has been found by the studies made by the present inventorsthat reduction in the weight of the handle by thinning the handle piperesults in a change in the level of comfort of riding, which may fatiguethe rider.

The present invention made in light of the above-described problem hasan object of reducing the weight of a handle of a straddled vehiclewhile alleviating the fatigue of the rider.

SUMMARY OF THE INVENTION

A handle for a straddled vehicle in an embodiment according to thepresent invention includes a first handle grip and a second handle gripgraspable by a rider; and a tube-like handle pipe supporting the firsthandle grip and the second handle grip. The handle pipe includes anattachment portion located in a central portion in a longitudinaldirection, the attachment portion being attachable to a steeringrotation device; a first grip portion located at one of two ends in thelongitudinal direction, the first grip portion having the first handlegrip attached thereto; a second grip portion located at the other of thetwo ends in the longitudinal direction, the second grip portion havingthe second handle grip attached thereto; a first bent portion locatedbetween the attachment portion and the first grip portion, the firstbent portion extending from one of two ends of the attachment portion toone of two ends of the first grip portion, the first bent portionextending in a direction different from a direction in which theattachment portion extends; and a second bent portion located betweenthe attachment portion and the second grip portion, the second bentportion extending from the other end of the two ends of the attachmentportion to one of two ends of the second grip portion, the second bentportion extending in a direction different from the direction in whichthe attachment portion extends. The first grip portion includes a firstoverlapping region overlapping the first handle grip and a firstnon-overlapping region located between the first overlapping region andthe first bent portion, the first non-overlapping region not overlappingthe first handle grip; the second grip portion includes a secondoverlapping region overlapping the second handle grip and a secondnon-overlapping region located between the second overlapping region andthe second bent portion, the second non-overlapping region notoverlapping the second handle grip; the first non-overlapping region ofthe first grip portion and the second non-overlapping region of thesecond grip portion each include a thick portion having a thicknesslarger than, or equal to, a thickness of the attachment portion; and thefirst overlapping region of the first grip portion and the secondoverlapping region of the second grip portion each include a thinportion having a thickness smaller than the thickness of the thickportion.

In an embodiment, the thickness of the thin portion is smaller than thethickness of the attachment portion.

In an embodiment, the thin portion is provided such that the firstoverlapping region of the first grip portion and the second overlappingregion of the second grip portion each have a mass that is 12% or lessof a mass of the entirety of the handle pipe.

In an embodiment, where a border between the first overlapping regionand the first non-overlapping region of the first grip portion is afirst border, and a border between the second overlapping region and thesecond non-overlapping region of the second grip portion is a secondborder, the thin portion in the first overlapping region is providedfrom the other of the two ends of the first grip portion to apredetermined first position; the thin portion in the second overlappingregion is provided from the other of the two ends of the second gripportion to a predetermined second position; and a distance between thefirst position and the first border and a distance between the secondposition and the second border are each 30 mm or less.

In an embodiment, the thin portion is provided in substantially theentirety of each of the first overlapping region and the secondoverlapping region.

In an embodiment, the thickness of the thin portion is smaller than thethickness of the thick portion in the entirety of a circumferentialdirection of the handle pipe.

In an embodiment, the thickness of the thin portion is smaller than thethickness of the thick portion partially in a circumferential directionof the handle pipe.

In an embodiment, the thickness of the thin portion is substantially thesame in the longitudinal direction of the handle pipe, and issymmetrical.

In an embodiment, the thickness of the thin portion is changed in thelongitudinal direction of the handle pipe.

In an embodiment, there is no weight member located in the first gripportion or the second grip portion.

In an embodiment, the handle pipe is formed of a non-iron metalmaterial.

In an embodiment, the attachment portion of the handle pipe has an outerdiameter larger than an outer diameter of each of the first grip portionand the second grip portion.

In an embodiment, the first bent portion and the second bent portioneach have a flattening of 5% or less in a central portion thereof.

A straddled vehicle in an embodiment according to the present inventionincludes the handle for a straddled vehicle having any of theabove-described structures.

A method for producing a handle pipe for a straddled vehicle in anembodiment according to the present invention is a method for producingthe handle pipe including an attachment portion located in a centralportion in a longitudinal direction, the attachment portion beingattachable to a steering rotation device; a first grip portion locatedat one of two ends in the longitudinal direction; a second grip portionlocated at the other of the two ends in the longitudinal direction; afirst bent portion located between the attachment portion and the firstgrip portion, the first bent portion extending from one of two ends ofthe attachment portion to one of two ends of the first grip portion, thefirst bent portion extending in a direction different from a directionin which the attachment portion extends; and a second bent portionlocated between the attachment portion and the second grip portion, thesecond bent portion extending from the other end of the two ends of theattachment portion to one of two ends of the second grip portion, thesecond bent portion extending in a direction different from thedirection in which the attachment portion extends. The method includesstep (A) of preparing a tube-like workpiece formed of a metal material;step (B) of processing the workpiece such that an outer diameter of eachof regions of the workpiece to be the first grip portion and the secondgrip portion is smaller than an outer diameter of a region of theworkpiece to be the attachment portion; step (C) of processing theworkpiece with solution heat treatment after the step (B); and step (D)of bending the workpiece after the step (C).

In an embodiment the workpiece prepared in the step (A) is a workpieceproduced by extrusion.

In an embodiment, the method further includes step (E) of partiallythinning each of the regions of the workpiece to be the first gripportion and the second grip portion. The first grip portion and thesecond grip portion each include a thick portion having a thicknesslarger than, or equal to, a thickness of the attachment portion and athin portion having a thickness smaller than the thickness of the thickportion.

In an embodiment, the step (E) is performed by machining after the step(B).

In an embodiment, the step (B) is performed by swaging; and the step (E)is performed in the step (B).

In the handle for a straddled vehicle in an embodiment according to thepresent invention, the first grip portion and the second grip portion ofthe handle pipe each include the thick portion having a thickness largerthan, or equal to, a thickness of the attachment portion, and the thinportion having a thickness smaller than the thickness of the thickportion. Specifically, the thick portion is provided in the firstnon-overlapping region (region not overlapping the first handle grip) ofthe first grip portion and the second non-overlapping region (region notoverlapping the second handle grip) of the second grip portion.Specifically, the thin portion is formed in the first overlapping region(region overlapping the first handle grip) of the first grip portion andthe second overlapping region (region overlapping the second handlegrip) of the second grip portion. Since the first grip portion and thesecond grip portion each include the thick portion, the handle certainlyprovides a sense of sufficient rigidity. Since the first grip portionand the second grip portion each include the thin portion, the handle ismade more lightweight than in a case where, for example, the first gripportion and the second grip portion are entirely the thick portion. Inthe case where the thick portion is located in each of relatively innerregions of the first grip portion and the second grip portion (the firstnon-overlapping region and the second non-overlapping region) and thethin portion is located in each of relatively outer regions of the firstgrip portion and the second grip portion (the first overlapping regionand the second overlapping region), the sense of being pushed up isdecreased. Therefore, fatigue of the rider is reduced. As describedabove, an embodiment according to the present invention reduces theweight of the handle for a straddled vehicle while alleviating thefatigue of the rider.

In the case where the thickness of the thin portion is smaller than thethickness of the attachment portion, the handle is more lightweight.

From the point of view of providing a sufficient effect of reducing theweight of the handle and the point of view of decreasing the sense ofbeing pushed up with more certainty, it is preferred that the thinportions are provided such that the mass of each of the firstoverlapping region of the first grip portion and the second overlappingregion of the second grip portion is 12% or less of the entire mass ofthe handle pipe.

From the point of view of reducing the weight of the handle, it ispreferred that the thin portion is as large as possible in each of thefirst overlapping region and the second overlapping region. For example,the thin portion in the first overlapping region may be provided from anend of the first grip portion (end opposite to the first bent portion)to a predetermined position (first position). The thin portion in thesecond overlapping region may be provided from an end of the second gripportion (end opposite to the second first bent portion) to apredetermined position (second position). Where the border between thefirst overlapping region and the first non-overlapping region in thefirst grip portion is referred to as a “first border”, and a borderbetween the second overlapping region and the second non-overlappingregion in the second grip portion is referred to as a “second border”,it is preferred that the distance between the first position and thefirst border, and the distance between the second position and thesecond border, are each 30 mm or less.

In the case where the thin portion is provided in substantially theentirety of each of the first overlapping region and the secondoverlapping region, the sufficient effect of reducing the weight is moreeasily provided.

In the case where the thickness of the thin portion is smaller than thethickness of the thick portion in the entirety of a circumferentialdirection of the handle pipe (namely, the handle pipe is thinned in theentirety of the circumferential direction thereof), the effect ofreducing the weight is higher than in the case where the handle pipe isthinned partially in the circumferential direction.

In the case where the thickness of the thin portion is smaller than thethickness of the thick portion partially in the circumferentialdirection, the flexural rigidity of the first grip portion and thesecond grip portion is easily adjusted.

The thickness of each thin portion may be substantially the same in thelongitudinal direction of the handle pipe and may be symmetrical, or maychange in the longitudinal direction of the handle pipe.

The handle for a straddled vehicle in an embodiment according to thepresent invention does not need to include a weight member in the firstgrip portion or the second grip portion.

An embodiment according to the present invention has significance in thecase where the handle pipe is formed of a non-iron metal material. Thereason is as follows. In the case where the handle pipe is formed of aniron-based material such as steel or the like, it is difficult to reducethe weight of the handle pipe by decreasing the thickness because thehandle pipe formed of an iron-based material is already thin. Bycontrast, in the case where the handle pipe is formed of a non-ironmetal material, the handle pipe may need to be entirely thick in orderto have a requisite level of rigidity under the restrictions on theshape required by the posture of the rider riding the motorcycle. In anembodiment according to the present invention, the relatively largethickness is well utilized (more specifically, the thin portion isselectively formed as described above), so that the requisite level ofrigidity is satisfied while the fatigue of the rider is alleviated.

An embodiment according to the present invention is preferablyapplicable to a handle in which the outer diameter of the attachmentportion of the handle pipe is larger than the outer diameter of each ofthe first grip portion and the second grip portion (so-called taperedhandle). In the case where a handle pipe for such a tapered handle isproduced by, for example, swaging, the thickness of the handle pipebecomes larger from the central portion (attachment portion) toward theends. This easily increases the weight of the handle pipe. In anembodiment according to the present invention, the first grip portionand the second grip portion of the handle pipe each include the thinportion. This preferably realizes a lightweight tapered handle.

From the point of view of uniformizing the rigidity, it is preferredthat the flattening of each of the first bent portion and the secondbent portion is low. Specifically, it is preferred that the first bentportion and the second bent portion each have a flattening of 5% or lessin the central portion thereof.

According to the method in an embodiment of the present invention, thesolution heat treatment is performed before the bending. In the casewhere the solution heat treatment is performed after the bending, theworkpiece is kept at a high temperature and then is rapidly cooled afterbeing molded into a product shape. Thus, the workpiece is significantlydeformed by the heat treatment. This requires the workpiece to becorrected after being processed with the solution heat treatment. Bycontrast, in an embodiment according to the present invention, thesolution heat treatment is performed before the bending. Therefore, theworkpiece does not need to be corrected. In addition, the workpiece isbent after becoming hard to a certain degree by the solution heattreatment. Therefore, the cross-sectional shape of the first bentportion and the second bent portion is not easily changed. This allowsthe flattening of the first bent portion and the second bent portion tobe low.

The prepared workpiece is preferably a workpiece produced by extrusion(extruded member), and is more preferably a workpiece produced byhydrostatic pressure extrusion (hydrostatic pressure-extruded member).The extruded member has a highly uniform thickness. The hydrostaticpressure-extruded member has a higher strength than that of a generalextruded member.

The regions of the workpiece to be the first grip portion and the secondgrip portion may partially be thinned. In the case where the first gripportion and the second grip portion each include the thick portionhaving the thickness larger than, or equal to, the thickness of theattachment portion and the thin portion having the thickness smallerthan the thickness of the thick portion, the handle is reduced in weightand the fatigue of the rider is suppressed.

The step of partially thinning the regions to be the first grip portionand the second grip portion may be preferably performed by, for example,machining.

The method for producing the handle in an embodiment according to thepresent invention includes a step of processing the workpiece such thatthe outer diameter of the regions of the workpiece to be the first gripportion and the second grip portion is smaller than the outer diameterof the region of the workpiece to be the attachment portion (diametercontraction step). The diameter contraction step may be preferablyperformed by, for example, swaging. In such a case, the regions to bethe first grip portion and the second grip portion may partially bethinned in the diameter contraction step.

An embodiment according to the present invention reduces the weight ofthe handle for a straddled vehicle and also alleviates the fatigue ofthe rider.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side view showing a schematic structure of a motorcycle(straddled vehicle) 1 in an embodiment according to the presentinvention.

FIG. 2A, FIG. 2B and FIG. 2C are respectively a plan view, a left sideview and a rear view as seen obliquely from above, of a handle 20 of themotorcycle 1.

FIG. 3A, FIG. 3B and FIG. 3C are respectively a plan view, a left sideview and a rear view as seen obliquely from above, of a handle pipe 22of the handle 20.

FIG. 4 shows cross-sections of an attachment portion AP, a first gripportion GP1 and a second grip portion GP2 of the handle pipe 22(cross-section taken along a longitudinal direction of the handle pipe22).

FIG. 5A and FIG. 5B are cross-sectional views showing an example ofstructure of the first grip portion GP1 and the second grip portion GP2.

FIG. 6A and FIG. 6B are cross-sectional views showing an example ofstructure of the first grip portion GP1 and the second grip portion GP2.

FIG. 7A and FIG. 7B are cross-sectional views showing an example ofstructure of the first grip portion GP1 and the second grip portion GP2.

FIG. 8A and FIG. 8B are cross-sectional views showing an example ofstructure of the first grip portion GP1 and the second grip portion GP2.

FIG. 9A and FIG. 9B are cross-sectional views showing an example ofstructure of the first grip portion GP1 and the second grip portion GP2.

FIG. 10A, FIG. 10B and FIG. 10C each show an example of shapes of afirst overlapping region GPla and a second overlapping region GP2 a in across-section perpendicular to the longitudinal direction of the handlepipe 22.

FIG. 11 is a flowchart showing a method for producing the handle pipe22.

FIG. 12 is a flowchart showing a method for producing a handle pipe in areference example.

FIG. 13 is a graph showing an example of stress-strain curve of aworkpiece formed of an aluminum alloy after the workpiece is annealedand after the workpiece is processed with solution heat treatment.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. The present invention is not limited toany of the following embodiments.

(Overall Structure of the Motorcycle)

FIG. 1 is a left side view showing a schematic structure of a motorcycle(straddled vehicle) 1. The motorcycle 1 is a vehicle for motocross,which is assumed to run on a rough terrain. As shown in FIG. 1, themotorcycle 1 includes a vehicle frame 2, an engine 3, a front wheel 4, arear wheel 5, a seat 6, a fuel tank 7, and a handle 20. In the followingdescription, the terms “front”, “rear”, “left” and “right” respectivelyrefer to front, rear, left and right as seen from a rider (driver)sitting on the seat 6 while gripping the handle 20.

The vehicle frame 2 is a cradle-type frame, and supports the engine 3.The vehicle frame 2 includes a first main frame 10 a, a second mainframe 10 b, a down frame 11, a first bottom frame 12 a, a second bottomframe 12 b, a head pipe 13, a pair of rear arms 14 a and 14 b, a firstrear arm 15 a, and a second rear arm 15 b.

The head pipe 13 is located in a front part of the motorcycle 1. Thefirst main frame 10 a and the second main frame 10 b are located side byside in a vehicle width direction (left-right direction). The first mainframe 10 a and the second main frame 10 b extend obliquely rearward anddownward from the head pipe 13.

The first main frame 10 a is located in a left part of the motorcycle 1,and the second main frame 10 b is located in a right part of themotorcycle 1. A pivot shaft 16 is provided at bottom ends of the firstmain frame 10 a and the second main frame 10 b.

The down frame 11 is connected with the head pipe 13 at a position lowerthan a position at which the first main frame 10 a and the second mainframe 10 b is connected with the head pipe 13. The down frame 11 extendsrearward and downward from the head pipe 13.

The first bottom frame 12 a connects a bottom end of the down frame 11and a bottom end of the first main frame 10 a to each other. The secondbottom frame 12 b connects the bottom end of the down frame 11 and abottom end of the second main frame 10 b to each other.

With the above-described structure, as seen from the left side of themotorcycle 1, the head pipe 13, the first main frame 10 a, the downframe 11 and the first bottom frame 12 a are connected in a loop. Asseen from the right side of the motorcycle 1, the head pipe 13, thesecond main frame 10 b, the down frame 11 and the second bottom frame 12b are also connected in a loop.

The pair of rear arms 14 a and 14 b are respectively located in the leftpart and the right part of the motorcycle 1. The pair of rear arms 14 aand 14 b have front ends each attached to the pivot shaft 16, and aresupported by the pivot shaft 16 so as to be swingable upward anddownward. The rear wheel 5 is held in the vehicle width directionbetween, and rotatably attached to, rear ends of the pair of rear arms14 a and 14 b.

The first rear frame 15 a is located in the left part of the motorcycle1, whereas the second rear frame 15 b is located in the right part ofthe motorcycle 1. The first rear frame 15 a has a front end connectedwith the first main frame 10 a, and extends rearward from the first mainframe 10 a. The second rear frame 15 b has a front end connected withthe second main frame 10 b, and extends rearward from the second mainframe 10 b.

The head pipe 13 supports a steering device 30 such that the steeringdevice 30 is rotatable. The steering device 30 is capable of changingthe advancing direction of the motorcycle 1. The steering device 30includes a steering rotation device 31 and the handle 20. The steeringrotation device 31 includes a steering shaft (not shown), an upperbracket 8, an under bracket 9, a front suspension 17, and the frontwheel 4. A top end, of the steering shaft (not shown), located in thehead pipe 13 is attached to the upper bracket 8, and a bottom end of thesteering shaft is attached to the under bracket 9. The upper bracket 8and the under bracket 9 each have left and right ends that retain a topportion of the front suspension 17. The front wheel 4 is rotatablyattached to a bottom end of the front suspension 17. The handle 20 isattached to the upper bracket 8. The steering device 30 is structuredsuch that an operation, performed by the rider gripping the handle 20,of rotating the handle 20 around the steering shaft results in arotation of the steering rotation device 31 around the steering shaft,which changes an orientation of the front wheel 4.

The seat 6 is located above the first main frame 10 a and the secondmain frame 10 b and to the rear of the head pipe 13. The fuel tank 7 islocated below the seat 6. The engine 3 is located below the first mainframe 10 a and the second main frame 10 b and to the rear of the downframe 11.

(Structure of the Handle)

With reference to FIG. 2A, FIG. 2B and FIG. 2C, a structure of thehandle 20 will be described. FIG. 2A, FIG. 2B and FIG. 2C arerespectively a plan view, a left wide view, and a rear view as seenobliquely from above, of the handle 20. FIG. 2A, FIG. 2B and FIG. 2Calso show the upper bracket 8.

As shown in FIG. 2A, FIG. 2B and FIG. 2C, the handle 20 includes a pairof handle grips (first handle grip and second handle grip) 21A and 21B,and a handle pipe (also referred to as a “handle bar”) 22. The handle 20may further include a lever (clutch lever or brake lever), a switch unitand the like, which are omitted in these figures.

The first handle grip 21A and the second handle grip 21B are graspableby the rider. The first handle grip 21A and the second handle grip 21Bare each cylindrical and are formed of, for example, rubber. Brims 21Afand 21Bf are respectively provided at ends (inner ends) of the firsthandle grip 21A, and the second handle grip 21B.

The handle pipe 22 is tube-like (namely, is hollow), and is typicallyformed of a metal material. The handle pipe 22 supports the first handlegrip 21A and the second handle grip 21B.

The handle pipe 22 includes an attachment portion AP, a pair of gripportions (first grip portion and second grip portion) GP1 and GP2, and apair of bent portions (first bent portion and second bent portion) BP1and BP2.

The attachment portion AP is at a central portion of the handle pipe 22in a longitudinal direction. The attachment portion AP extends generallystraight. The attachment portion AP is to be attached to the steeringrotation device 31. In the example shown in the figures, the attachmentportion AP is attached to the upper bracket 8 via a pair or clampmembers 18. The structure usable to attach the attachment portion AP tothe steering rotation device 31 is not limited to that described above.For example, the attachment portion AP may be attached to the steeringrotation device 31 via one clamp member.

The first grip portion GP1 is located at one of two ends of the handlepipe 22 in the longitudinal direction (in this example, at the leftend). The first grip portion GP1 extends generally straight. The firstgrip portion GP1 extends in the vehicle width direction in the statewhere the steering device 30 is oriented in the front-rear direction(hereinafter, referred to as a “vehicle straight advancing state”) ofthe motorcycle 1. In the vehicle straight advancing state, a left end ofthe first grip portion GP1 is located to the rear of, and above, theattachment portion AP. At the left end of the first grip portion GP1,the first handle grip 21A is attached.

The second grip portion GP2 is located at the other of the two ends ofthe handle pipe 22 in the longitudinal direction (in this example, atthe right end). The second grip portion GP2 extends generally straight.The second grip portion GP2 extends in the vehicle width direction inthe vehicle straight advancing state. In the vehicle straight advancingstate, a right end of the second grip portion GP2 is located to the rearof, and above, the attachment portion AP. At the right end of the secondgrip portion GP2, the second handle grip 21B is attached.

The first bent portion BP1 is located between the attachment portion APand the first grip portion GP1. The first bent portion BP1 extends fromone of two ends of the attachment portion AP to a right end of the firstgrip portion GP1, and in a direction different from the direction inwhich the attachment portion AP extends. More specifically, the firstbent portion BP1 extends upward and rearward. The first bent portion BP1connects the attachment portion AP and the first grip portion GP1 toeach other.

The second bent portion BP2 is located between the attachment portion APand the second grip portion GP2. The second bent portion BP2 extendsfrom the other of the two ends of the attachment portion AP to a leftend of the second grip portion GP2, and in a direction different fromthe direction in which the attachment portion AP extends. Morespecifically, the second bent portion BP2 extends upward and rearward.The second bent portion BP2 connects the attachment portion AP and thesecond grip portion GP2 to each other.

In this example, outer diameter od1 (see FIG. 2A) of the attachmentportion AP is larger than outer diameter od2 of each of the first gripportion GP1 and the second grip portion GP2. Namely, the handle 20 is aso-called tapered handle.

Now, with reference also to FIG. 3A, FIG. 3B and FIG. 3C, the structureof the handle pipe 22 included in the handle 20 will be described inmore detail. FIG. 3A, FIG. 3B and FIG. 3C respectively correspond toFIG. 2A, FIG. 2B and FIG. 2C, but show only the handle pipe 22.

As shown in FIG. 3A, FIG. 3B and FIG. 3C, the first grip portion GP1includes a first overlapping region GP1 a and a first non-overlappingregion GP1 b. The first overlapping region GP1 a is a region overlappingthe first handle grip 21A. The first non-overlapping region GP1 b islocated between the first overlapping region GP1 a and the first bentportion BP1 and does not overlap the first handle grip 21A.

Similarly, the second grip portion GP2 includes a second overlappingregion GP2 a and a second non-overlapping region GP2 b. The secondoverlapping region GP2 a is a region overlapping the second handle grip21B. The second non-overlapping region GP2 b is located between thesecond overlapping region GP2 a and the second bent portion BP2 and doesnot overlap the second handle grip 21B.

Hereinafter, the first overlapping region GP1 a and the secondoverlapping region GP2 a may be collectively referred to as “overlappingregions”. The first non-overlapping region GP1 b and the secondnon-overlapping region GP2 b may be collectively referred to as“non-overlapping regions”.

Now, with reference to FIG. 4, the thickness relationship among thecomponents of the handle pipe 22 will be described. FIG. 4 showscross-sections of the attachment portion AP, the first grip portion GP1and the second grip portion GP2, taken along the longitudinal directionof the handle pipe 22.

The first non-overlapping region GP1 b of the first grip portion GP1 andthe second non-overlapping region GP2 b of the second grip portion GP2each include a thick portion p1 having thickness t1, which is largerthan, or equal to, thickness t0 of the attachment portion AP.

The first overlapping region GP1 a of the first grip portion GP1 and thesecond overlapping region GP2 a of the second grip portion GP2 eachinclude a thin portion p2 having thickness t2, which is smaller thanthickness t1 of the thick portion p1. In this example, thickness t2 ofthe thin portion p2 is smaller than thickness t0 of the attachmentportion AP.

The first bent portion BP1 and the second bent portion BP2 typicallyhave a thickness larger than, or equal to, thickness t0 of theattachment portion AP. In the case where swaging described below is usedto produce the handle pipe 22, the thickness of the first bent portionBP1 gradually increases from an end thereof close toward the attachmentportion AP toward an end thereof close to the first grip portion GP1.Similarly, the thickness of the second bent portion BP2 graduallyincreases from an end thereof close to the attachment portion AP towardan end thereof close to the second grip portion GP2.

As described above, in the handle 20 in this embodiment, the first gripportion GP1 and the second grip portion GP2 of the handle pipe 22 eachinclude the thick portion p1 having thickness t1 larger than, or equalto, thickness t0 of the attachment portion AP, and the thin portion p2having thickness t2 smaller than thickness t1 of the thick portion p1.Specifically, the thick portion p1 is provided in the non-overlappingregion GP1 b of the first grip portion GP1 and the non-overlappingregion GP2 b of the second grip portion GP2. Specifically, the thinportion p2 is formed in the overlapping region GP1 a of the first gripportion GP1 and the overlapping region GP2 a of the second grip portionGP2. Since the first grip portion GP1 and the second grip portion GP2each include the thick portion p1, the handle pipe 22 certainly providesa sense of sufficient rigidity. Since the first grip portion GP1 and thesecond grip portion GP2 each include the thin portion p2, the handlepipe 22 is made more lightweight than in a case where, for example, thefirst grip portion GP1 and the second grip portion GP2 are entirely thethick portion p1. It has been found by the studies made by the presentinventors that in the case where the thick portion p1 is located in eachof relatively inner regions of the grip portions GP1 and GP2 (firstnon-overlapping region GP1 b and second non-overlapping region GP2 b)and the thin portion p2 is located in each of relatively outer regionsof the grip portions GP1 and GP2 (first overlapping region GP1 a andsecond overlapping region GP2 a), fatigue of the rider is reduced. Aconceivable reason for this is that the above-described thicknessdistribution decreases the sense of being pushed up and provides apreferable sense of operation.

It was investigated in which case such a preferable sense of operationwould be provided, and a reason for this was estimated. Results thereofwill be described.

Handles in an example and comparative examples 1 through 3 were producedby use of an aluminum alloy as a metal material. An investigation wasperformed on the sense of operation. Table 1 shows the results. Theinvestigation was performed on three items: the sense of being pushedup, the sense of steerability, and the sense of rigidity. Theinvestigation was performed as follows. A motorcycle including thehandle in the example and comparative examples 1 through 3 was caused bya rider to run on a rugged surface, and the rider made evaluations. Inthe example and comparative examples 1 through 3, the thickness of theattachment portion and the thickness of the grip portions are as shownin Table 2. As shown in Table 2, in comparative examples 1 through 3,the entirety of the grip portions (i.e., the overlapping regions and thenon-overlapping regions) has the same thickness. By contrast, in theexample, the thickness of the overlapping regions (length of eachoverlapping region in the longitudinal direction is 113 mm) is smallerthan the thickness of the non-overlapping regions. Table 2 also showsthe weight of the entirety of the handle pipe and the weight of theoverlapping region of each grip portion in the example and comparativeexamples 1 through 3.

TABLE 1 SENSE OF SENSE OF SENSE OF BEING RIGIDITY STEERABILITY PUSHED UPEXAMPLE 2.9 3.2 3 COMPARATIVE 3 3 3 EXAMPLE 1 COMPARATIVE 2.7 3.1 2.8EXAMPLE 2 COMPARATIVE 2.5 3 2.8 EXAMPLE 3

TABLE 2 THICKNESS OF GRIP PORTION WEIGHT OF THICKNESS OF NON-OVER- OVER-WEIGHT OF OVER- ATTACHMENT LAPPING LAPPING HANDLE LAPPING PORTION REGIONREGION PIPE REGION EXAMPLE 3.2 mm 4.3 mm 3.0 mm 536 g 58 g COMPARATIVE4.0 mm 4.0 mm 644 g 72 g EXAMPLE 1 COMPARATIVE 3.2 mm 4.0 mm 564 g 72 gEXAMPLE 2 COMPARATIVE 3.2 mm 4.3 mm 577 g 76 g EXAMPLE 3

The sense of operation was evaluated based on comparative example 1. Incomparative example 1, the handle pipe is heaviest, but the handleprovides no problem in the sense of operation. In comparative example 2,the handle pipe is more lightweight than in comparative example 1, butthe handle is inferior to that in comparative example 1 on the sense ofbeing pushed up and the sense of rigidity. In comparative example 3, thehandle pipe is more lightweight than in comparative example 1, but thehandle is inferior to that in comparative example 1 on the sense ofbeing pushed up and the sense of rigidity.

By contrast, in the example, the handle pipe is significantly morelightweight than in comparative example 1, and the handle issubstantially equal to that in comparative example 1 on the sense ofbeing pushed up and the sense of rigidity and is superior to that incomparative example 1 on the sense of steerability.

As seen from above, it has been confirmed that since the overlappingregions GP1 a and GP2 a of the grip portions GP1 and GP2 each includethe thin portion p2, the handle is more lightweight and provides apreferable sense of operation. It is presumed that the sense ofrigidity, the sense of being pushed up and the sense of steerability areimproved by thinning the overlapping regions GP1 a and GP2 a for thefollowing reasons.

[Sense of Rigidity]

When applying a load to the grip portions via the handle grip, the ridersenses a displacement behavior of the grip portions. A displacementbehavior of the grip portions in response to the load that is too smallor too large is not felt to be preferable by the rider. A displacementof the grip portions that is appropriate is felt to be preferable by therider. In the case where the thin portions are located in theoverlapping regions of the grip portions and the thick portions arelocated in the non-overlapping regions of the grip portions, anappropriate displacement is realized and a preferable sense of rigidityis provided.

[Sense of being Pushed Up]

While a motorcycle is running on a rugged surface, the handle vibrates.The rider senses the vibration behavior of the grip portions as a senseof being pushed up. In the case where the vibration is large or theattenuation of the vibration is slow, the rider feels that the sense ofbeing pushed up is large. As a parameter showing the attenuation of thevibration, logarithmic decrement is known. The logarithmic decrement δis represented by the following expression by use of damping ratio ζ.

δ=2πζ

As represented by the following expression, the damping ratio ζ is theratio of damping coefficient C and the critical damping coefficient Cc.

ζ=C/Cc

The critical damping coefficient Cc is represented by the followingexpression by use of the mass m of the mass point and the springconstant k.

Cc=2(mk)^(1/2)

Therefore, as the mass m is smaller, or as the spring constant k issmaller, the logarithmic decrement δ is larger and the attenuation isquicker.

Applying the above to the vibration of the handle, it is considered thatas the ends of the grip portions (i.e., overlapping regions) have asmaller mass and have a lower rigidity, the attenuation of the vibrationis quicker. Therefore, in the case where the overlapping region of eachgrip portion includes the thin portion, the attenuation is quicker andthus the rider feels that the sense of being pushed up is alleviated.

[Sense of Steerability]

In the case where a portion far from the gravitational center of avehicle is more lightweight, the moment of inertia is smaller, and thusthe rider feels the weight less easily when inclining the vehicle orkeeping the posture of the vehicle. Therefore, in the case where theoverlapping region of the grip portions located at each of the two endsof the handle is thinned, the sense of steerability is improved.

As described above, in an embodiment according to the present invention,the weight is reduced without sacrificing the sense of operation.Therefore, the weight of the handle is reduced while the fatigue of therider is alleviated.

Hereinafter, preferred structures of the handle 20 in this embodimentand modifications thereof will be described.

Thickness t2 of the thin portion p2 is preferably smaller than thicknesst0 of the attachment portion AP. In the case where thickness t2 of thethin portion p2 is smaller than thickness t0 of the attachment portionAP, the handle 20 is more lightweight.

As understood from the above, the balance of the rigidity of the handle20 and the weight of the ends thereof is considered to influence thesense of operation. The ratio of the weight of the overlapping regionsGP1 a and GP2 a with respect to the total weight of the handle pipe 22may be set to a predetermined range, so that a preferred sense ofoperation is provided with certainty. The studies made by the presentinventors have found it preferable to provide that the thin portion p2in each of the first overlapping region GP1 a and the second overlappingregion GP2 a is such that the weight (mass) of each of the firstoverlapping region GP1 a and the second overlapping region GP2 a is 12%or less of the total weight (mass) of the handle pipe 22. Table 3 belowshows the results of an investigation made on the relationship betweenthe ratio of the weight of each overlapping region with respect to theweight of the handle pipe and the sense of operation. Table 3 shows theratio of the weight of each overlapping region with respect to theweight of the handle pipe (weight ratio) and the evaluation results onthe sense of operation regarding each of the example and comparativeexamples 1 through 9, on which the studies were made. Regarding thesense of operation, “◯” indicates that the sense of operation ispreferred, and “x” indicates that the sense of operation is notpreferred. Table 3 also shows the weight of each overlapping region, thetotal weight of the handle pipe, and the thickness of each of theattachment portion and the grip portions (overlapping regions andnon-overlapping regions).

TABLE 3 WEIGHT [g] WEIGHT THICKNESS [mm] OVERLAPPING RATIO ATTACHMENTNON-OVERLAPPING OVERLAPPING EVALUATION TOTAL REGION [%] PORTION REGIONREGION RESULTS EXAMPLE 536 58 10.8 3.2 4.3 3 ∘ COMPARATIVE 644 72 11.2 44 4 ∘ EXAMPLE 1 COMPARATIVE 564 72 12.8 3.2 4 4 x EXAMPLE 2 COMPARATIVE577 76 13.2 3.2 4.3 4.3 x EXAMPLE 3 COMPARATIVE 544 72 13.2 3 4 4 xEXAMPLE 4 COMPARATIVE 464 57 12.3 3 3 3 x EXAMPLE 5 COMPARATIVE 504 5711.3 3 3 3 x EXAMPLE 6 COMPARATIVE 528 57 10.8 3.2 3 3 x EXAMPLE 7COMPARATIVE 555 57 10.3 3.4 3 3 x EXAMPLE 8 COMPARATIVE 518 54 10.4 3.42.8 2.8 x EXAMPLE 9

Referring to Table 3, the example is compared against comparativeexamples 2 through 5. It is seen from the comparison that in the casewhere the ratio of the weight of the overlapping region with respect tothe weight of the entirety of the handle pipe is 12% or less, apreferred sense of operation is provided. In comparative examples 6through 9, the ratio of the weight of the overlapping region withrespect to the weight of the entirety of the handle pipe is 12% or less,but a preferred sense of operation is not provided. A conceivable reasonfor this is that the grip portions do not include a thick portion thatis thicker than, or equal to, the attachment portion (comparativeexamples 7 through 9) or that the grip portions do not include a thinportion that is thinner than the thick portion (comparative example 6).

As shown in FIG. 5A and FIG. 5B, the thin portion p2 may be provided insubstantially the entirety of each of the first overlapping region GP1 aand the second overlapping region GP2 a. In the case where the thinportion p2 is provided in substantially the entirety of each of thefirst overlapping region GP1 a and the second overlapping region GP2 a,a sufficient effect of reducing the weight of the handle pipe 22 is moreeasily provided. A border (stepped portion) between the thick portion p1and the thin portion p2 may have a rounded corner in the cross-sectionor may not have a rounded corner in the cross-section as shown in FIG.5A and FIG. 5B.

FIG. 5A and FIG. 5B show a structure in which the thin portions p2 eachhave substantially the same thickness in the longitudinal direction ofthe handle pipe 22, and the thickness is symmetrical with respect to thecentral axis. The handle pipe 22 is not limited to having such astructure. As shown in FIG. 6A and FIG. 6B, the thickness of the thinportions p2 may change in the longitudinal direction of the handle pipe22. In the example shown in FIG. 6A and FIG. 6B, the thickness of eachthin portion p2 decreases from the inner side (closer to the bentportion adjacent to the grip portion) toward the outer side.

As shown in FIG. 7A and FIG. 7B, the first overlapping region GP1 a andthe second overlapping region GP2 a may each include a portion that isnot the thin portion p2 (e.g., portion that is as thick as the thickportion p1). In the structure shown in FIG. 7A, the thin portion p2 inthe first overlapping region GP1 a is provided from the end of the firstgrip portion GP1 (end opposite to the first bent portion BP1) to apredetermined position (first position) 11. In the structure shown inFIG. 7B, the thin portion p2 in the second overlapping region GP2 a isprovided from the end of the second grip portion GP2 (end opposite tothe second bent portion BP2) to a predetermined position (secondposition) 12. From the point of view of providing a sufficient effect ofreducing the weight of the handle pipe 22, it is preferred that the thinportion p2 is as large as possible in each of the first overlappingregion GP1 and the second overlapping region GP2. Border bd1 between thefirst overlapping region GP1 a and the first non-overlapping region GP1b in the first grip portion GP1 will be referred to as a “first border”,and border bd2 between the second overlapping region GP2 a and thesecond non-overlapping region GP2 b in the second grip portion GP2 willbe referred to as a “second border”. From the point of view of reducingthe weight of the handle pipe 22, it is preferred that distance d1between the first position 11 and the first border bd1, and distance d2between the second position 12 and the second border bd2, are each 30 mmor less.

As shown in FIG. 8A and FIG. 8B, the thin portion p2 may be provided toextend into each of the first non-overlapping region GP1 b and thesecond non-overlapping region GP2 b. In the structure shown in FIG. 8A,the thin portion p2 is provided from the end of the first grip portionGP1 (end opposite to the first bent portion BP1) to a predeterminedposition (third position) 13 in the first non-overlapping region GP1 b.In the structure shown in FIG. 8B, the thin portion p2 is provided fromthe end of the second grip portion GP2 (end opposite to the second bentportion BP2) to a predetermined position (fourth position) 14 in thesecond non-overlapping region GP2 b. From the point of view of rigidity,it is preferred that distance d3 between the third position 13 and thefirst border bd1, and distance d4 between the fourth position 14 and thesecond border bd2, are each 30 mm or less.

As shown in FIG. 9A and FIG. 9B, the thickness of each of the gripportions GP1 and GP2 may not be smallest at the outer end (end notconnected with the bent portion). In the structure shown in FIG. 9A, thefirst overlapping region GP1 a includes a portion p3, which is not thethin portion p2 (i.e., which does not have a thickness smaller than thatof the thick portion p1), at the outer end thereof. The portion p3 hasan outer diameter smaller than an outer diameter of the thin portion p2.In the structure shown in FIG. 9B, the second overlapping region GP2 aincludes a portion p3, which is not the thin portion p2 (i.e., whichdoes not have a thickness smaller than that of the thick portion p1), atthe outer end thereof. The portion p3 has an outer diameter smaller thanthe outer diameter of the thin portion p2. As described above, the firstoverlapping region GP1 a and the second overlapping region GP2 a mayeach include the thin portion p2 in at least a part thereof.

FIG. 10A, FIG. 10B and FIG. 10C each show an example of shape of theoverlapping regions GPla and GP2 a in a cross-section perpendicular tothe longitudinal direction of the handle pipe 22. In FIG. 10A, FIG. 10Band FIG. 10C, the thick portions p1 in the non-overlapping regions GP1 band GP2 b are represented by the dashed line.

In the example shown in FIG. 10A, the thickness of the thin portion p2is smaller than the thickness of the thick portion p2 in the entirety ofthe circumferential direction of the handle pipe 22. In the case wherethe handle pipe 22 is thinned in the entirety of the circumferentialdirection, the effect of reducing the weight of the handle 20 is higherthan in the case where the handle pipe 22 is thinned partially in thecircumferential direction.

In each of the examples shown in FIG. 10B and FIG. 10C, the thickness ofthe thin portion p2 is smaller than the thickness of the thick portionp1 partially in the circumferential direction. In the example shown inFIG. 10B, portions having a small thickness and portions having a largethickness (portions as thick as the thick portion p1) are alternatelylocated in the circumferential direction. In the example shown in FIG.10C, the thickness of the thin portion p2 is continuously increased anddecreased in repetition in the circumferential direction. An innercircumferential surface has a spline-curve profile. Such a structure inwhich the thickness is decreased partially in the circumferentialdirection has an advantage that the flexural rigidity of the first gripportion GP1 and the second grip portion GP2 is easily adjusted.

Conventionally, a structure in which a weight member is attached to agrip portion of a handle of a motorcycle in order to decrease thevibration is known. The handle 20 in this embodiment does not need toinclude an attached weight member to be located in the first gripportion GP1 or the second grip portion GP2.

The handle pipe 22 may be preferably formed of a non-iron metal materialsuch as an aluminum alloy, a magnesium alloy or the like. An embodimentaccording to the present invention has significance in the case wherethe handle pipe 22 is formed of a non-iron metal material. In the casewhere the handle pipe 22 is formed of an iron-based material such assteel or the like, it is difficult to reduce the weight of the handle 20by decreasing the thickness because the handle pipe 22 formed of aniron-based material is already thin. In the case where the handle pipe22 is formed of a composite material, it is very costly and requires ahuge amount of energy to produce the handle pipe 22. By contrast, in thecase where the handle pipe 22 is formed of a non-iron metal material,the handle pipe 22 may need to be entirely thick in order to have arequisite level of rigidity under the restrictions on the shape requiredby the posture of the rider riding the motorcycle 1. In an embodimentaccording to the present invention, the relatively large thickness iswell utilized (more specifically, the thin portion p2 is selectivelyformed as described above), so that the requisite level of rigidity issatisfied while the fatigue of the rider is alleviated.

Now, with reference to FIG. 11, a method for producing the handle pipe22 in this embodiment will be described. FIG. 11 is a flowchart showingan example of method for producing the handle pipe 22.

First, a tube-like workpiece is prepared (step S1). In this step, aworkpiece formed of an aluminum alloy is prepared. For example, aworkpiece processed with hydrostatic pressure extrusion (hydrostaticpressure-extruded member) is prepared, and the prepared workpiece isprocessed with drawing. The “hydrostatic pressure extrusion” is a typeof extrusion molding. According to the hydrostatic pressure extrusion, abillet is not extruded directly, but is extruded via a liquid (fluid)having an appropriate level of viscosity. As a workpiece, an extrudedmember other than the hydrostatic pressure-extruded member (e.g., memberformed by direct extrusion or indirect extrusion), or a drawn member maybe used. The drawn member has a high size precision. An extruded memberused as a workpiece has a uniform thickness. The above-describedhydrostatic pressure-extruded member used as a workpiece has a higherstrength than a general extruded member. In the case where thehydrostatic pressure-extruded member is processed with drawing, theresultant workpiece has a still higher size precision. Such a workpiecehas little change in the section modulus and is deformed more uniformly.The workpiece prepared in this step (after being processed with thedrawing) has a constant outer diameter and a constant inner diameter(i.e., constant thickness) in the entirety thereof. A preferably usableexample of aluminum alloy may be Al—Mg-Zu-Cu-based aluminum alloy.

Next, the workpiece is processed such that regions of the workpiece thatare to be the first grip portion GP1 and the second grip portion GP2have an outer diameter smaller than an outer diameter of a region thatis to be the attachment portion AP (diameter contraction). In this step,swaging is performed (step S2). The diameter contraction (raising) maybe performed by a method other than swaging (e.g., by spinning).

Then, the regions of the workpiece that are to be the first grip portionGP1 and the second grip portion GP2 are partially thinned (step S3). Thethinning step may be preferably performed by, for example, machining(e.g., cutting).

Next, the workpiece is processed with solution heat treatment (step S4).The temperature and the time duration of the solution heat treatment areset in accordance with the composition of the aluminum alloy. Forexample, the solution heat treatment is performed at 470 to 480° C. for1 to 3 hours.

Then, the workpiece is bent (step S5). As a result of the bending, thefirst bent portion BP1 and the second bent portion BP2 are formed.

Next, the workpiece is processed with artificial aging (step S6). Forexample, the artificial aging is performed at 115 to 125° C. for 3 to 6hours and then at 170 to 180° C. for 6 to 12 hours. The solution heattreatment and the artificial aging may be collectively referred to as a“T7 heat treatment”. In this embodiment, the bending is performedbetween the solution heat treatment and the artificial aging in the T7heat treatment.

Next, the workpiece is processed with shot peening (step S7). The shotpeening is performed in order to improve the fatigue strength.

Then, the workpiece is anodized (step S8). The anodization is a step offorming an anodized film on a surface of the aluminum alloy.

As a result, the handle pipe 22 is formed. The method for producing thehandle pipe 22 in this embodiment provides an effect that the first bentportion BP1 and the second bent portion BP2 have a low level offlattening. Hereinafter, a reason for this will be described.

FIG. 12 is a flowchart showing a method for producing a handle pipe in areference example. According to the method in the reference example, thehandle pipe is produced as follows. First, an extruded member isprepared as a workpiece (step S11), and then, the workpiece is processedwith drawing (step S12).

Next, the workpiece is swaged (step S13), and then is annealed in orderto be softened (step S14).

Next, the workpiece is bent (step S15), and then is processed withsolution heat treatment (step S16). Then, the workpiece is corrected(step S17).

Next, the workpiece is sequentially processed with artificial aging(step S18), shot peening (step S19) and anodization (step S20).

According to the method in the reference example, the workpiece isprocessed with the solution heat treatment (step S16) after being bent(step S15). Therefore, after being molded into a product shape, theworkpiece is kept at a high temperature and then is rapidly cooled.Thus, the workpiece is significantly deformed by the heat treatment.This requires the workpiece to be corrected (step S17) after beingprocessed with the solution heat treatment.

By contrast, according to the method in this embodiment, the workpieceis processed with the solution heat treatment (step S4) before beingbent (step S5). Therefore, the workpiece does not need to be corrected.In addition, the workpiece is bent after becoming hard to a certaindegree by the solution heat treatment. Therefore, the cross-sectionalshape of the first bent portion BP1 and the second bent portion BP2 isnot easily changed. This allows the flattening of the first bent portionBP1 and the second bent portion BP2 to be low. The “flattening” isdefined as (maximum diameter−minimum diameter)×100/average diameter. Inthe case where the flattening is high, the rigidity difference, whichdepends on the load direction, is increased. From the point of view ofuniformizing the rigidity, it is preferred that the flattening of eachof the first bent portion BP1 and the second bent portion BP2 is low.Specifically, it is preferred that the first bent portion BP1 and thesecond bent portion BP2 each have a flattening of 5% or less in acentral portion thereof. Also according to the method in thisembodiment, the annealing is not necessary. This decreases the time andenergy for the production of the handle pipe 22.

Even after being processed with the solution heat treatment, theworkpiece is bent with no problem for the following reason. Theworkpiece, even though becoming hard to a certain degree by the solutionheat treatment, may have a sufficient level of plastic deformability.FIG. 13 shows an example of stress-strain curve of a workpiece formed ofan aluminum alloy after the workpiece is annealed and after theworkpiece is processed with the solution heat treatment. It is seen fromFIG. 13 that even after the workpiece is processed with the solutionheat treatment, the yield ratio, which is obtained by division of theyield point by the tensile strength, is low. This shows that theworkpiece has a sufficient level of plastic deformability.

As shown in FIG. 11, it is preferred to prepare the workpiece producedby hydrostatic pressure extrusion (hydrostatic pressure-extrudedmember). A reason for this is that the hydrostatic pressure-extrudedmember has a higher strength than that of a general extruded member, andthus may be thinned to be still more lightweight.

In the example shown in FIG. 11, the thinning is performed between theswaging and the solution heat treatment. The timing at which theworkpiece is thinned is not limited to such a timing. The thinning maybe performed between the artificial aging and the shot peening, betweenthe shot peening and the anodization, or after the anodization.

At the time of swaging, the regions to be the overlapping regions GP1 aand GP2 a may be made thinner than the regions to be the non-overlappingregions GP1 b and GP2 b. Namely, the thinning may be performed at thesame time with the swaging. For example, a stepped core bar including aportion having a relatively large outer diameter (large-diameterportion) and a portion having a relatively small outer diameter(small-diameter portion) is prepared, and the swaging is performed suchthat inner circumferential surfaces of the portions of the workpiecethat are to be the grip portions GP1 and GP2 contact the stepped corebar. In this manner, the thick portion p1 is formed around thesmall-diameter portion, and the thin portion p2 is formed around thelarge-diameter portion.

An embodiment according to the present invention is preferablyapplicable to a handle in which the attachment portion AP of the handlepipe 22 has the outer diameter larger than the outer diameter of thegrip portions GP1 and GP2 (so-called tapered handle). In the case wherea handle pipe for such a tapered handle is produced by, for example,swaging, the thickness of the handle pipe becomes larger from thecentral portion (attachment portion) toward the ends. This easilyincreases the weight of the handle pipe. In an embodiment according tothe present invention, the first grip portion GP1 and the second gripportion GP2 of the handle pipe 22 each include the thin portion p2. Thispreferably realizes a lightweight tapered handle.

An embodiment according to the present invention is not limited to beingapplicable to a tapered handle. Namely, an embodiment according to thepresent invention is applicable to a handle in which the outer diameterof the grip portions GP1 and GP2 is the same as the outer diameter ofthe attachment portion AP.

The above-described description is regarding a motorcycle as an exampleof straddled vehicle. The straddled vehicle is not limited to themotorcycle. The handle in an embodiment according to the presentinvention is preferably applicable to any of various straddled vehiclesincluding a bicycle, a snow mobile, an ATV (All Terrain Vehicle), apersonal water craft and the like. In the case of being applied to sucha vehicle, the handle in an embodiment according to the presentinvention is preferably usable for a steering device capable of changingthe advancing direction of the straddled vehicle.

As described above, in the handle 20 for a straddled vehicle in anembodiment according to the present invention, the first grip portionGP1 and the second grip portion GP2 of the handle pipe 22 each includethe thick portion p1 having thickness t1 larger than, or equal to,thickness t0 of the attachment portion AP and the thin portion p2 havingthickness t2 smaller than thickness t1 of the thick portion p1.Specifically, the thick portion p1 is provided in the firstnon-overlapping region GP1 b (portion not overlapping the first handlegrip 21A) of the first grip portion GP1 and in the secondnon-overlapping region GP2 b (portion not overlapping the second handlegrip 21B) of the second grip portion GP2. Specifically, the thin portionp2 is provided in the first overlapping region GP1 a (portionoverlapping the first handle grip 21A) of the first grip portion GP1 andin the second overlapping region GP2 a (portion overlapping the secondhandle grip 21B) of the second grip portion GP2. The first grip portionGP1 and the second grip portion GP2 each include the thick portion p1,and thus the handle 20 has a sense of sufficient rigidity withcertainty. The first grip portion GP1 and the second grip portion GP2each include the thin portion p2, and thus the handle 20 is morelightweight than in the case where, for example, the first grip portionGP1 and the second grip portion GP2 are each entirely the thick portionp1. The thick portion p1 is provided in a relatively inner region ofeach of the first grip portion GP1 and the second grip portion GP2(first non-overlapping region GP1 b and the second non-overlappingregion GP2 b), and the thin portion p2 is provided in a relatively outerregion of each of the first grip portion GP1 and the second grip portionGP2 (first overlapping region GP1 a and the second overlapping regionGP2 a). Thus, the sense of being pushed up is decreased. This reducesthe fatigue of the rider. As described above, an embodiment according tothe present invention reduces the weight of the handle 20 for astraddled vehicle and also alleviates the fatigue of the rider.

In the case where thickness t2 of the thin portion p2 is smaller thanthickness t0 of the attachment portion AP, the handle 20 is morelightweight.

From the point of view of providing a sufficient effect of reducing theweight of the handle 20 and the point of view of decreasing the sense ofbeing pushed up with more certainty, it is preferred that the thinportions p2 are provided such that the mass of each of the firstoverlapping region GP1 a of the first grip portion GP1 and the secondoverlapping region GP2 a of the second grip portion GP2 is 12% or lessof the entire mass of the handle pipe 22.

From the point of view of reducing the weight of the handle 20, it ispreferred that the thin portion p2 is as large as possible in each ofthe first overlapping region GP1 a and the second overlapping region GP2a. For example, the thin portion p2 in the first overlapping region GP1a may be provided from the end of the first grip portion GP1 (endopposite to the first bent portion BP1) to the predetermined position(first position) 11. The thin portion p2 in the second overlappingregion GP2 a may be provided from the end of the second grip portion GP2(end opposite to the second first bent portion BP2) to the predeterminedposition (second position) 12. Where border bd1 between the firstoverlapping region GP1 a and the first non-overlapping region GP1 b inthe first grip portion GP1 is referred to as the “first border”, andborder bd2 between the second overlapping region GP2 a and the secondnon-overlapping region GP2 b in the second grip portion GP2 is referredto as the “second border”, it is preferred that distance d1 between thefirst position 11 and the first border bd1, and distance d2 between thesecond position 12 and the second border bd2, are each 30 mm or less.

In the case where the thin portion p2 is provided in substantially theentirety of each of the first overlapping region GP1 a and the secondoverlapping region GP2 a, the sufficient effect of reducing the weightis more easily provided.

In the case where the thickness of the thin portion p2 is smaller thanthe thickness of the thick portion p1 in the entirety of thecircumferential direction of the handle pipe 22 (namely, the handle pipe22 is thinned in the entirety of the circumferential direction thereof),the effect of reducing the weight is higher than in the case where thehandle pipe 22 is thinned partially in the circumferential direction.

In the case where the thickness of the thin portion p2 is smaller thanthe thickness of the thick portion p1 partially in the circumferentialdirection, the flexural rigidity of the first grip portion GP1 and thesecond grip portion GP2 is easily adjusted.

The thickness of each thin portion p2 may be substantially the same inthe longitudinal direction of the handle pipe 22 and may be symmetrical,or may change in the longitudinal direction of the handle pipe 22.

The handle 20 for a straddled vehicle in an embodiment according to thepresent invention does not need to include a weight member in the firstgrip portion GP1 or the second grip portion GP2.

An embodiment according to the present invention has significance in thecase where the handle pipe 22 is formed of a non-iron metal material.The reason is as follows. In the case where the handle pipe 22 is formedof an iron-based material such as steel or the like, it is difficult toreduce the weight of the handle pipe 22 by decreasing the thicknessbecause the handle pipe 22 formed of an iron-based material is alreadythin. By contrast, in the case where the handle pipe 22 is formed of anon-iron metal material, the handle pipe 22 may need to be entirelythick in order to have a requisite level of rigidity under therestrictions on the shape required by the posture of the rider ridingthe motorcycle 1. In an embodiment according to the present invention,the relatively large thickness is well utilized (more specifically, thethin portion p2 is selectively formed as described above), so that therequisite level of rigidity is satisfied while the fatigue of the rideris alleviated.

An embodiment according to the present invention is preferablyapplicable to a handle in which outer diameter od1 of the attachmentportion AP of the handle pipe 22 is larger than outer diameter od2 ofeach of the first grip portion GP1 and the second grip portion GP2(so-called tapered handle). In the case where a handle pipe for such atapered handle is produced by, for example, swaging, the thickness ofthe handle pipe becomes larger from the central portion (attachmentportion) toward the ends. This easily increases the weight of the handlepipe. In an embodiment according to the present invention, the firstgrip portion GP1 and the second grip portion GP2 of the handle pipe 22each include the thin portion p2. This preferably realizes a lightweighttapered handle.

From the point of view of uniformizing the rigidity, it is preferredthat the flattening of each of the first bent portion BP1 and the secondbent portion BP2 is low. Specifically, it is preferred that the firstbent portion BP1 and the second bent portion BP2 each have a flatteningof 5% or less in the central portion thereof.

According to the method in an embodiment of the present invention, thesolution heat treatment is performed before the bending. In the casewhere the solution heat treatment is performed after the bending, theworkpiece is kept at a high temperature and then is rapidly cooled afterbeing molded into a product shape. Thus, the workpiece is significantlydeformed by the heat treatment. This requires the workpiece to becorrected after being processed with the solution heat treatment. Bycontrast, in an embodiment according to the present invention, thesolution heat treatment is performed before the bending. Therefore, theworkpiece does not need to be corrected. In addition, the workpiece isbent after becoming hard to a certain degree by the solution heattreatment. Therefore, the cross-sectional shape of the first bentportion BP1 and the second bent portion BP2 is not easily changed. Thisallows the flattening of the first bent portion BP1 and the second bentportion BP2 to be low.

The prepared workpiece is preferably a workpiece produced by extrusion(extruded member), and is more preferably a workpiece produced byhydrostatic pressure extrusion (hydrostatic pressure-extruded member).The extruded member has a highly uniform thickness. The hydrostaticpressure-extruded member has a higher strength than that of a generalextruded member.

The regions of the workpiece to be the first grip portion GP1 and thesecond grip portion GP2 may partially be thinned. In the case where thefirst grip portion GP1 and the second grip portion GP2 each include thethick portion p1 having thickness t1 larger than, or equal to, thicknesst0 of the attachment portion AP and the thin portion p2 having thicknesst2 smaller than thickness t1 of the thick portion p1, the handle 20 isreduced in weight and the fatigue of the rider is reduced.

The step of partially thinning the regions to be the first grip portionGP1 and the second grip portion GP2 may be preferably performed by, forexample, machining.

The method for producing the handle 20 in an embodiment according to thepresent invention includes a step of processing the workpiece such thatthe outer diameter of the regions of the workpiece to be the first gripportion GP1 and the second grip portion GP2 is smaller than the outerdiameter of the region of the workpiece to be the attachment portion AP(diameter contraction step). The diameter contraction step may bepreferably performed by, for example, swaging. In such a case, theregions to be the first grip portion GP1 and the second grip portion GP2may partially be thinned in the diameter contraction step.

An embodiment according to the present invention reduces the weight ofthe handle for a straddled vehicle and also alleviates the fatigue ofthe rider. A handle for a straddled vehicle in an embodiment accordingto the present invention is preferably usable for any of variousstraddled vehicles.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

What is claimed is:
 1. A handle for a straddled vehicle, comprising: a first handle grip and a second handle grip graspable by a rider; and a tube-like handle pipe supporting the first handle grip and the second handle grip; wherein: the handle pipe includes: an attachment portion located in a central portion in a longitudinal direction, the attachment portion being attachable to a steering rotation device; a first grip portion located at one of two ends of the handle pipe in the longitudinal direction, the first grip portion having the first handle grip attached thereto; a second grip portion located at another of the two ends of the handle pipe in the longitudinal direction, the second grip portion having the second handle grip attached thereto; a first bent portion located between the attachment portion and the first grip portion, the first bent portion extending from one of two ends of the attachment portion to one of two ends of the first grip portion, the first bent portion extending in a direction different from a direction in which the attachment portion extends; and a second bent portion located between the attachment portion and the second grip portion, the second bent portion extending from another end of the two ends of the attachment portion to one of two ends of the second grip portion, the second bent portion extending in a direction different from the direction in which the attachment portion extends; wherein: the first grip portion includes a first overlapping region overlapping the first handle grip and a first non-overlapping region located between the first overlapping region and the first bent portion, the first non-overlapping region not overlapping the first handle grip; the second grip portion includes a second overlapping region overlapping the second handle grip and a second non-overlapping region located between the second overlapping region and the second bent portion, the second non-overlapping region not overlapping the second handle grip; the first non-overlapping region of the first grip portion and the second non-overlapping region of the second grip portion each include a thick portion having a thickness larger than, or equal to, a thickness of the attachment portion; and the first overlapping region of the first grip portion and the second overlapping region of the second grip portion each include a thin portion having a thickness smaller than the thickness of the thick portion.
 2. The handle for a straddled vehicle according to claim 1, wherein the thickness of the thin portion is smaller than the thickness of the attachment portion.
 3. The handle for a straddled vehicle according to claim 1, wherein the thin portion is provided such that the first overlapping region of the first grip portion and the second overlapping region of the second grip portion each have a mass that is 12% or less of a mass of an entirety of the handle pipe.
 4. The handle for a straddled vehicle according to claim 1, wherein where a border between the first overlapping region and the first non-overlapping region of the first grip portion is a first border, and a border between the second overlapping region and the second non-overlapping region of the second grip portion is a second border, the thin portion in the first overlapping region is provided from another of the two ends of the first grip portion to a predetermined first position; the thin portion in the second overlapping region is provided from another of the two ends of the second grip portion to a predetermined second position; and a distance between the first position and the first border and a distance between the second position and the second border are each 30 mm or less.
 5. The handle for a straddled vehicle according to claim 1, wherein the thin portion is provided in substantially an entirety of each of the first overlapping region and the second overlapping region.
 6. The handle for a straddled vehicle according to claim 1, wherein the thickness of the thin portion is smaller than the thickness of the thick portion in an entirety of a circumferential direction of the handle pipe.
 7. The handle for a straddled vehicle according to claim 1, wherein the thickness of the thin portion is smaller than the thickness of the thick portion partially in a circumferential direction of the handle pipe.
 8. The handle for a straddled vehicle according to claim 1, wherein the thickness of the thin portion is substantially a same thickness in the longitudinal direction of the handle pipe, and is symmetrical with respect to a central axis of the handle pipe.
 9. The handle for a straddled vehicle according to claim 1, wherein the thickness of the thin portion changes in the longitudinal direction of the handle pipe.
 10. The handle for a straddled vehicle according to claim 1, wherein there is no weight member located in the first grip portion or the second grip portion.
 11. The handle for a straddled vehicle according to claim 1, wherein the handle pipe is formed of a non-iron metal material.
 12. The handle for a straddled vehicle according to claim 1, wherein the attachment portion of the handle pipe has an outer diameter larger than an outer diameter of each of the first grip portion and the second grip portion.
 13. The handle for a straddled vehicle according to claim 1, wherein the first bent portion and the second bent portion each have a flattening of 5% or less in a central portion thereof.
 14. A straddled vehicle, comprising the handle for a straddled vehicle according to claim
 1. 15. A method for producing a handle pipe for a straddled vehicle, the handle pipe including: an attachment portion located in a central portion in a longitudinal direction, the attachment portion being attachable to a steering rotation device; a first grip portion located at one of two ends of the handle pipe in the longitudinal direction; a second grip portion located at another of the two ends of the handle pipe in the longitudinal direction; a first bent portion located between the attachment portion and the first grip portion, the first bent portion extending from one of two ends of the attachment portion to one of two ends of the first grip portion, the first bent portion extending in a direction different from a direction in which the attachment portion extends; and a second bent portion located between the attachment portion and the second grip portion, the second bent portion extending from another end of the two ends of the attachment portion to one of two ends of the second grip portion, the second bent portion extending in a direction different from the direction in which the attachment portion extends; the method comprising: a step (A) of preparing a tube-like workpiece formed of a metal material; a step (B) of processing the workpiece such that an outer diameter of each of regions of the workpiece to be the first grip portion and the second grip portion is smaller than an outer diameter of a region of the workpiece to be the attachment portion; a step (C) of processing the workpiece with solution heat treatment after the step (B); and a step (D) of bending the workpiece after the step (C).
 16. The method for producing a handle pipe for a straddled vehicle according to claim 15, wherein the workpiece prepared in the step (A) is a workpiece produced by extrusion.
 17. The method for producing a handle pipe for a straddled vehicle according to claim 15, further comprising a step (E) of partially thinning each of the regions of the workpiece to be the first grip portion and the second grip portion; wherein the first grip portion and the second grip portion each include a thick portion having a thickness larger than, or equal to, a thickness of the attachment portion and a thin portion having a thickness smaller than the thickness of the thick portion.
 18. The method for producing a handle pipe for a straddled vehicle according to claim 17, wherein the step (E) is performed by machining after the step (B).
 19. The method for producing a handle pipe for a straddled vehicle according to claim 17, wherein: the step (B) is performed by swaging; and the step (E) is performed in the step (B). 